The forward voltage drop (on voltage) between the drain and the source of the field effect transistor (SiC-MOSFET) with the metal-oxide-semiconductor junction structure (MOS) including a wide bandgap semiconductor, particularly silicon carbide (SiC), can be set to be smaller than that of the MOSFET (Si-MOSFET) including silicon carbide (Si). Thus, the number of unit cells and the size of chips of the SiC-MOSFET can be set to be smaller than those of the Si-MOSFET. For example, a 50% reduction in on resistance can result in a 50% reduction in the number of unit cells and a 50% reduction in the size of chips.
The area of the gate of the SiC-MOSFET is accordingly reduced, and thus, the capacitance component between the gate and the source is reduced, causing a reduction in the tolerance to electrostatic discharge damage (ESD) between the gate and the source.
In general, as a measure against electrostatic discharge damage, the Si-MOSFET has included a Zener diode connected between the gate and the source in some cases as disclosed in, for example, Patent Document 1. The Zener diode (poly-Zener diode) has been formed, as the p-n junction layer on the polysilicon (poly-Si) layer being the material of the gate electrode, through the source formation process (n-type diffusion layer formation process) and the P+ diffusion process (p-type diffusion layer formation process) in the formation of unit cells.